The answer for a is $\displaystyle -\frac{1}{3}P + \frac{560}{3}$. However, I do not see how they arrived at that answer. Any help will be greatly appreciated.A charter airline finds that on its Saturday flights from Philadelphia to London, all 120 seats will be sold if the ticket price is $200. However, for each $3 increase in ticket price, the number of seats sold decreases by one.

a) Find a formula for the number of seats sold if the ticket price isPdollars.